1. Technical Field
The present invention relates generally to silane compositions, processes for their preparation and rubber compositions containing same.
2. Description of the Related Art
The tire treads of modem tires must meet performance standards which require a broad range of desirable properties. Generally, three types of performance standards are important in tread compounds. They include good wear resistance, good traction and low rolling resistance. Major tire manufacturers have developed tire tread compounds which provide lower rolling resistance for improved fuel economy and better skid/traction for a safer ride. Thus, rubber compositions suitable for, e.g., tire treads, should exhibit not only desirable strength and elongation, particularly at high temperatures, but also good cracking resistance, good abrasion resistance, desirable skid resistance and low tangent delta values at low frequencies for desirable rolling resistance of the resulting treads. Additionally, a high complex dynamic modulus is necessary for maneuverability and steering control.
Presently, silica has been added to rubber compositions as a filler to replace some or substantially all of the carbon black filler to improve these properties, e.g., lower rolling resistance. Although more costly than carbon black, the advantages of silica include, for example, improved wet traction, low rolling resistance, etc., with reduced fuel consumption. However, as compared to carbon black, there tends to be a lack of, or at least an insufficient degree of, physical and/or chemical bonding between the silica particles and the rubber to enable the silica to become a reinforcing filler for the rubber thereby giving less strength to the rubber. Therefore, a silica filler system typically requires the use of coupling agents.
Generally, coupling agents are used to enhance the rubber reinforcement characteristics of silica. Such coupling agents, for example, may be premixed or pre-reacted with the silica particles or added to the rubber mix during the rubber/silica processing, or mixing, stage. If the coupling agent and silica are added separately to the rubber mix during the rubber/silica processing, or mixing, stage, it is considered that the coupling agent then combines in situ with the silica.
A coupling agent is typically a bi-functional molecule that will react with the silica at one end thereof and cross-link with the rubber at the other end. In this manner, the reinforcement and strength of the rubber, e.g., the toughness, strength, modulus, tensile and abrasion resistance, are particularly improved. The coupling agent is believed to cover the surface of the silica particle which then hinders the silica from agglomerating with other silica particles. By interfering with the agglomeration process, the dispersion is improved and therefore the wear and fuel consumption are also improved. Present coupling agents have several problems associated with them such as, for example, toxicity and compatibility problems with other ingredients employed in the rubber composition.
Accordingly, there exists a need for improved coupling agents.